The present invention relates generally to fluid pressure regulators, and more specifically, to two-stage pressure regulating valves convertible without parts replacement for use with LP or natural gas.
Applications have existed for some time for pressure regulating valves capable of regulating to either of two electrically selected pressures. In general, applications have been somewhat specialized, and the required volumes relatively small, thus providing little incentive for exploring nontraditional designs. To the extent two-stage pressure regulator valve designs are known, they generally employ a solenoid actuator to control the force supplied by a regulator spring.
A pressure regulating valve application which has begun to receive increasing interest is in connection with fuel gas valves for small furnaces, such as those used in single family residences, including both permanent fixed location homes and mobile homes. Certain U.S. furnace manufacturers have developed high efficiency furnace designs which rely on two stages of furnace operation. When heat is first called for, and under moderate heat requirements, the furnace is fired at a low to moderate rate. If firing at that rate does not provide the heat output required for existing conditions, firing is stepped to a higher rate.
Another factor which impacts gas valve manufacturers and users is that both natural gas and gas produced from liquefied petroleum (LP) or propane are in common use as fuel gases. These gases have different burning characteristics, and are supplied to a furnace or other burner apparatus under different pressures. Specifically, gas generated from liquefied petroleum has a faster flame front. Accordingly, it is supplied to a burner at a higher pressure, e.g., 10 inches H.sub.2 O, which induces more oxygen entrainment. In contrast, natural gas is typically supplied to a furnace or burner at a pressure of 3.5 inches H.sub.2 O. Accordingly, a pressure regulating gas valve :for a furnace or other appliance must regulate to a higher pressure for LP gas than for natural gas.
There are various situations in which it is not known at the outset which type of fuel gas will be used, and/or in which the type of fuel gas may be changed at some point during the operating life of the furnace or other appliance. Either situation often occurs with a mobile home. Another common situation is in connection with new construction of permanent fixed location dwellings. Initially natural gas may not be available because underground gas lines are not in place in the area, or because hook up to natural gas lines is delayed by frozen ground, or for other reasons.
Typical solutions in the past have been to either change out the entire gas valve at the time of conversion to a different fuel gas, or to replace certain components such as regulator springs or pressure regulator modules. Both of these solutions are undesirable for several reasons. Further, mobile home requirements now dictate that gas valve conversion be achievable without replacement of gas valve parts.
Although gas valves are available for two-stage operation, and gas valves are available which provide for conversion without parts replacement, an increasing need exists for a single gas valve which achieves both objectives. The applicant has devised a design for such a valve which retains the advantageous features of prior limited purpose designs, while adding the capability of both two-stage operation and no parts replacement conversion in a single unit.